This disclosure relates to the embossing of polymeric surfaces, and the articles formed thereby.
Optical, magnetic, and magneto-optic media are primary sources of high performance storage technology, allowing both high storage capacity and reasonable cost per megabyte of storage. One such type of media generally comprises a substrate covered by a polymer film. The film can be embossed to provide, for example, pits, grooves, asperities, bit patterns, servo-patterns, and edge features. The desired surface quality can also be embossed e.g., to obtain a desired smoothness, roughness, flatness, microwaviness, and texture, e.g., microtexturing for magnetic grain orientation. The embossed surface features can have a depth of up to about 200 nanometers (nm). Deeper features or features that vary outside the ranges can be produced, but, in general, for flying head applications, these can result in undesirable head-disk interactions. In the lateral dimension, the surface features, particularly of a magnetic data storage media, preferably have a “short” dimension of up to or exceeding about 250 nm, with less than about 200 nm more preferred, less than about 150 nm even more preferred, and less than about 100 nm especially preferred.
It is presently difficult to emboss polymer surfaces having high glass transition temperatures with nanometer-scale precision because extremely elevated temperatures (well above the glass transition) are required to ensure adequate flow and pattern replication. Under these conditions, there is potential to not only degrade the polymer surface, but also damage the substrate or surrounding sensitive layers and features.
When using either high or low glass transition polymers, another drawback associated with embossing methods such as hot stamping is the significant degree of adhesion that can develop between the embossed polymer surface and the stamping tool. This is particularly a problem when embossing at high temperatures. Such adhesion can lead to a number of problems, for example nanoscale defects and roughness, and gross defects such as film or stamper damage upon separation. Traditionally, adhesion of this type is mitigated through the use of mold release agents and other low surface energy molecules. These may be used as additives in the polymer, and/or applied topically to the mold surface and/or the surface of the polymer. While effective, these approaches are not often compatible with high temperature embossing processes, wherein the materials can undergo reaction and/or degradation at elevated temperature. The use of topically applied materials additionally necessitates reapplication after a relatively low number of molding cycles, adding to process cost and complexity. Finally, in the case of sub-micron replicated features, build-up of mold release additives can lead to poor feature replication.
There accordingly remains a need in the art for methods and materials that enable the embossing of polymeric surfaces without degradation, and/or with nanometer-scale precision, whether at high or low temperatures.